MBA 40mm Cloud Seeding Rocket, Sectioned


The sectioned rocket shown above is a Paul Smith masterpiece. It is an MBA 40mm Cloud Seeding Rocket, Type III, made in 1974 for the National Hail Research Experiment to see whether a payload of silver iodide (AgI) injected into a thunderstorm likely to produce crop-damaging hail could reduce or prevent the hail. The experiment and the rocket itself are covered in my book.

The rocket has a diameter of 42mm (1.65 inches) and a length of 219.5mm (8.64 inches). Its body is wrapped fiberglass. When I acquired this rocket and two others, this specimen had been cut into three pieces by the owner who was just curious about what it looked like inside. I couldn’t believe that someone would do this to a rare and very expensive collectible, but it turns out he did me a favor because I never would have asked Paul to section a complete round. However, this rocket had already been cut (carelessly and with a dull hacksaw, apparently), so seeing what Paul could make of it was the obvious thing to do. The result is a real stunner in my opinion.

With Paul’s three sectioned pieces in hand, I scanned each and combined them in Photoshop to create the image. At the back (right end of the image) you can see the steel nozzles held in place by aluminum bushings. Between the two nozzles shown, there is the Olin BWP bridgewire electric primer with extra primer composition added above the cup. Most of the motor section is taken up by the single propellant grain with an unusual threaded hole down the middle where the propellant ignites. Ahead of this you can see the aluminum delay train with a waterproofing seal at the back, a delay train igniter (gray), the delay train composition (almost white), and the explusion charge (almost black) in a chamber at the top of the aluminum assembly. Just ahead of the delay train, there is a waterproofing compound and then the silver iodide payload with an aluminum foil waterproofing seal just ahead of it. The nose windshield section is hollow.

When fired from an electric launcher outside the fuselage (body) of a small twin-engine aircraft flying under the base of the target thunderstorm, the electric bridgewire primer would ignite the primer composition which would ignite the propellant grain, launching the rocket up a long tube to allow it to spin up and accelerate prior to leaving the tube. As the propellant ignited, the delay train igniter lit the delay train, which allowed the rocket time to penetrate deep into the thunderstorm before the expulsion charge pushed the silver iodide up and out of the rocket case, where it dispersed in millions of microscopic pieces that the water in the thunderstorm could condense on and fall out as rain rather than build and freeze as hail. Pretty neat.

Paul Smith’s ability to do impossible sections must be limitless. Every time I ask him for something like this, he always does it to perfection.


This work is wonderful. Paul is a real artist. Mel, your scans are great too.


Excellent work on both hands.